The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Known vehicle powertrain system systems include one or more torque actuators coupled to transmissions that transfer torque to a driveline for tractive effort. Known torque actuators include internal combustion engines and electric motor/generators. An electric motor/generator may be used in a belt-alternator-starter (BAS) system as a torque actuator in place of an alternator. Known BAS systems include a serpentine belt to transfer torque between the engine and the electric motor/generator. Known BAS systems use a high-voltage energy storage system supplying high-voltage electrical power through a voltage inverter to the motor/generator unit.
Known transmissions include automatic transmissions which effect shifts in gear ratios to achieve a preferred match between an operator torque request, an engine operating point and a transmission gear ratio.
Known automatic transmissions execute upshifts to shift to a higher gear having a lower numerical multiplication ratio (gear ratio) and execute downshifts to shift to a lower gear having a higher numerical multiplication ratio. A transmission upshift requires a reduction in engine speed so the engine speed matches transmission output speed multiplied by the gear ratio at the target gear ratio. Known control systems reduce engine speed when executing an upshift event by reducing engine torque to minimize wear of transmission clutches. Known control systems act to increase engine torque at completion of an upshift event to provide greater engine torque to achieve constant axle torque at the lower gear ratio associated with the target gear ratio.
Known driver interpretation systems convert an operator torque request, e.g., an accelerator pedal position, into a desired amount of axle torque, engine power or engine torque. This operator torque request is translated into a crankshaft torque request to increase engine torque at completion of an upshift event, which provides an increase in engine torque to achieve a constant axle torque at the lower gear ratio associated with the target gear ratio. This crankshaft torque request may be in the form of a predicted and an immediate crankshaft torque request. A predicted crankshaft torque request is used to control actuators that respond with a slow, filtered response and preferably is an unfiltered indication of driver intent. On both compression-ignition engines and spark-ignition engines, the predicted torque request is used to control airflow actuators including turbochargers, throttles, cam phasers and EGR valves. An immediate crankshaft torque request is used to control actuators configured with fast accurate control. On a spark-ignition engine, fast actuators include spark ignition timing and fuel cutoff. Spark retard removes energy from combustion by producing heat instead of torque. Fuel cutoff may affect exhaust gas feedstream composition and emissions. Spark retard may affect fuel consumption. Thus, the immediate crankshaft torque request is preferably disabled under most driving situations. On a compression-ignition engine, the immediate torque request is controlled using fuel mass and injection timing. There is minimal penalty in emissions or fuel economy in using controlled fuel mass and injection timing to control to an immediate torque request. Thus, the immediate crankshaft torque request is preferably constantly enabled on a compression-ignition engine.
Known BAS systems arbitrate predicted and immediate crankshaft torque requests with predicted and immediate torque requests from other functions including requests associated with transmission shift torque management. Final arbitrated predicted and immediate torque requests are sent to an optimization system, which determines how to achieve the predicted and immediate crankshaft torque requests with available actuators in a fuel-efficient manner. The predicted crankshaft torque request is used to control engine airflow in conjunction with electric current flow to an electric torque machine to achieve the predicted crankshaft torque request. On a spark-ignition engine, an immediate crankshaft torque request that includes a reduction in torque is used to control spark timing and control electric regeneration using the electric torque machine, with priority given to using the electric torque machine at its maximum torque capacity for electric regeneration before using spark retard to absorb torque.
Known transmission shift control schemes generate an immediate crankshaft torque request at the beginning of the shift event that is used to reduce engine torque. The torque reduction during the shift event assists the transmission clutches in reducing engine speed. As engine speed is reduced, the crankshaft torque request increases to achieve a constant crankshaft power delivery at the end of the shift. A transmission shift control scheme uses the operator torque request during execution of a shift event to schedule clutch pressures to achieve the preferred magnitude of torque at the end of the shift. Toward the end of the shift event, the immediate crankshaft torque request ramps toward a possible crankshaft torque. The possible crankshaft torque is the torque that would have been achieved if the immediate crankshaft torque request were not commanded.
Known control systems generate a magnitude of possible crankshaft torque to indicate a magnitude of unmanaged crankshaft torque capacity at a present engine operating point when operating without constraints, i.e., without an immediate crankshaft torque request. This is known as air torque. The air torque is the magnitude of torque that an engine produces at a present measured/estimated air per cylinder, with optimum spark advance (or fuel injection timing) and with all cylinders being fueled. For a constant throttle position, the air per cylinder increases as the engine speed decreases to deliver a constant power under most operating positions.
A possible crankshaft torque during a shift event that is too high may cause a transmission controller to schedule too much clutch pressure and create a rough shift as the gears grab too quickly. A possible crankshaft torque during a shift event that is too low may cause a transmission controller to schedule too little clutch pressure and create clutch slipping because the clutches are unable to completely engage the spinning shaft at the end of a shift. Known control systems account for generator/alternator load as an accessory load that is subtracted from the possible crankshaft torque.